Recently, with the supply of smart phones and tablet PCs, and the activation of high capacity multimedia communication, the mobile traffic has been abruptly increasing. The mobile traffic increase is anticipated as about two fold annually in the future. Since most of the mobile traffic is transmitted through a base station, communication service providers are confronted with a problem of significant traffic load right now. In this reason, the communication service providers have been increased network facilities in order to process the increasing traffic and commercialized the next generation mobile communication standard such as mobile WIMAX and long term evolution (LTE) that enables large amount of traffic to process efficiently in a hurry. However, in order to cope with the amount of traffic that will be more abruptly increased in the future, another solution is required.
The device-to-device (D2D) direct communication is a distributed communication technique through which the traffic between adjacent nodes is directly forwarded not using the infrastructure such as a base station. In the D2D communication environment, each node such as a mobile terminal searches another terminal that is physically near with, and transmits traffic after setting up a communication session. Since the D2D communication may solve the problem of traffic overload by distributing the traffic that is concentrated on a base station, the D2D communication is highly favored as an element technology of the next generation mobile communication technology after 4G technology. For this reason, the standard group such as 3GPP or IEEE has been promoted the establishment of D2D communication standard based on LTE-A or Wi-Fi, and companies such as Qualcomm, and etc. have been developing the D2D communication technology independently.
The D2D communication is expected to create a new communication service as well as it contributes to improve the performance of mobile communication system. In addition, it may support the social network services based on proximity, network games, or the like. As such, the D2D technology is expected to provide new services in various fields.
The D2D communication technology that has been already widely utilized includes the infrared communication, the ZigBee, the radio frequency identification (RFID), the near field communication (NFC) based on this. However, since these technologies support the communication of special object within very limited distance (about 1 m) only, these technologies cannot be classified as the D2D communication technology through which the traffic of a base station is distributed, strictly.